USB Power Delivery (USB PD) along with Type-C specification aims at providing Universal Charger functionality where multiple different devices requiring different voltages and currents can be charged using a single USB PD charger. Even though universality is a key feature of USB PD Chargers, some charger designs requires recognition of a particular sink connected to it.

Any USB PD capable device is recognized through the combination of its VID and PID. VID refers to Vendor ID, which is allotted by USB-IF. PID refers to Product ID which is fixed by vendor for a particular product. This VID and PID information can be obtained from the sink by sending “Discover Identity VDM” message. Sink in response to this VDM message sends Acknowledgement which includes VID and PID of the sink device.

Following is the code snippet to send Discover Identity VDM message after the completion of PD negotiation between source and sink. The PD port is disabled if VID and PID of sink doesn’t match the expected values (expected sink device).

CYPD3171-24LQXQ_CLA project from CCGx Power SDK is used to test the code functionality.

bool send_discover_id(uint8_t port)
{
/* Format the command parameters.
Single DO with standard Discover_ID command to SOP controller.
Timeout is set to 100 ms.
*/
ccg_status_t stat;
cmd_buf.cmd_sop = SOP;
cmd_buf.cmd_do[0].val = 0xFF008001;
cmd_buf.no_of_cmd_do = 1;
cmd_buf.timeout = 100u;
/* Initiate the command. Keep trying until accepted. */
while ((stat = dpm_pd_command(port, DPM_CMD_SEND_VDM, 
    &cmd_buf, pd_command_cb)) != CCG_STAT_SUCCESS)
{
/* Can implement a timeout/abort here. */
if (abort_cmd)
return false;
}
/* Command has been queued. We cannot block for callback here. */
return true;
}

App event APP_EVT_PD_CONTRACT_NEGOTIATION_COMPLETE is triggered in app_event_handler function once the PD negotiation is complete. Discover Identity message is sent after negotiation complete event through a timer callback.

Attached to this post is the project which recognizes Ez-PD BCR as valid sink and turns the provider FET off when sinks other than BCR are connected. All changes to project are made in app.c file.

BJT Base drive	MOSFET gate drive
Current driven device	Voltage driven device
Current must be applied between the base and emitter terminals to produce a flow of current in the collector	MOSFET produces a flow of current in the drain when a voltage is applied between the gate and source terminals

• Gate Charge:
  • The gate of a MOSFET can be considered to be a capacitance.
  • The gate voltage of a MOSFET does not increase unless its gate input capacitance is charged, and the MOSFET does not turn on until its gate voltage reaches the gate threshold voltage Vth.
  • The gate threshold voltage Vth of a MOSFET is defined as the minimum gate bias required for creating a conduction channel between its source and drain regions.

• Input capacitance Ciss = Cgd + Cgs (gate to drain capacitance + gate to source capacitance)
• Output capacitance Coss = Cds + Cgd (drain to source capacitance + gate to drain capacitance)
• Reverse transfer capacitance Crss = Cgd (gate to drain capacitance)

• Calculating Gate drive resistance and Power consumed by the gate drive circuit:
  • Gate drive resistance:

1. Find out the total charge Qtotal (Gate to source and Gate to drain) and Gate driver voltage (Vg) from the datasheet of the MOSFET.
2. Total current through the gate path (coulomb/second) = Qtotal*Switching frequency
3. Gate driver resistance = Vg / (total current).
4. But to reduce gate loss we consider R = T/C, where T = Rise time (from datasheet).

• Power Consumed:

P = Ciss*(Vg)^2*fsw,

Where, Ciss = input capacitance.

            Vg = gate drive supply voltage.

            fsw = switching frequency.

• Different gate driving circuits:

     1. Basic circuit:

• Gate resistor R1: An appropriate resistor value should be selected because it affects the switching speed and therefore the switching loss of a MOSFET.
• PWM: It should be able to meet the following, A gate voltage sufficiently higher than Vth to turn on the MOSFET, voltage sufficiently lower than Vth to turn it off and a drive capability to sufficiently charge the input capacitance.
• Gate resistor R2: This resistor R2 is used to reduce the gate-source voltage to 0V when the input signal is open-circuited.

     2. Push Pull circuit:

• When the parasitic of MOSFET is relatively large and the PWM driving ability is no enough to drive MOSFET normally the below gate driving circuit is used.
• It consists of  Q2, Q3, VCC is used commonly to improve the driving ability.
• This circuit acts as a replacement to the digital logic circuit where the gate voltage is boosted.
• Boosting the logic gate voltage increases the power consumption of the circuit. Hence, we can use this circuit as a replacement.

     3. Accelerating Turn off time (Toff) of the MOSFET:

• During Ton, the gate current flows through R9 which is a high resistance path.
• Resistor R8 and diode D1 offer as low impedance path as possible to discharge the Cgs (gate to source capacitance) quickly when the MOSFET is transition to off state. This can reduce the turn off power loss of the MOSFET.
• Reducing R9 causes voltage spike and ringing effect. Hence a separate discharge path is designed with low impedance.

    4.

• There is one more circuit which is used to accelerate the discharge time of the MOSFET. It is as shown below,
• When the PWM signal has enough driving ability, Q7 is also used to discharge the Cgs (gate to source capacitance) quickly.
• D2 is used to prevent the discharge current flow back to PWM IC and damaging the IC.

     5. Pulse Transformer drive:

• By using a pulse transformer, the need for a separate drive power supply can be eliminated.
• It has a drawback in terms of the power consumption of a drive circuit.
• A pulse transformer is sometimes used to isolate a MOSFET from its driver in order to protect the drive circuit from the MOSFET’s fault.
• A Zener diode is added to quickly reset the transformer.

CYPD3174-16SXQ is targeted at Opto Coupler Feedback applications with a Opto Coupler Feedback Bootloader. It has a reduced pin list compared to CYPD3171 and CYPD3175.

It could also be used in directed feedback application with a modified hardware and firmware.

The schematic is shown below:

The firmware is derived from the CYPD3175-24LQXQ_pa_direct_fb with minor modifications. The only things changed are the device part number of bootloader and the project.

The following topics were discussed in brief in Part1 of this blog,

• Basic Definition of Power electronics.
• Different Applications of Power electronics.
• Various power electronic converters and their applications.
• Power Semiconductor Switching devices, their classification, and applications in power electronic converters.
• Basics of Linear Voltage Power Supply and Switched Mode Power Supply (SMPS).
• Block-level working of Fly-back converter.

Key takeaways from the following blog:

• Comparison between Linear and SMPS.
• USB power profiles.
• SMPS working.

1. Rectification stage: Considering with and without source inductance.
2. DC converter stage:

• Their role in SMPS.
• Isolated and Nonisolated topologies comparison.
• Steps to convert a non-isolated to its corresponding isolated topology.
• The main application of a switch in a DC-DC Converters.
• The basic working of a DC-DC converter using Inductor volt-sec and capacitor charge balance and small ripple approximation.
• Working of a closed-loop PWM.
• Buck-boost converter working.
• Reasons for the occurrence of discontinuity and their application.
• Working of Flyback converter
• Different modes of flyback converter their working and its advantages and disadvantages

The main motive behind this blog is to eventually build the understanding of Power Electronic Converters in USB applications. It comprises of different topics and concepts under one blog which are discussed in a proper sequential order to make everyone understand the application of PE who are new to this field.

Characteristic comparison of Linear and Switched Mode Power Supply (SMPS):

Inference: From the above comparison, we can conclude that SMPS is the best fit for USB power supplies based on the following characteristic: Efficiency, Voltage regulation, Magnetic material, weight, and copper requirement. 

USB standards and their power profiles:

Standard Voltage profiles associated with USB Power delivery: 5V, 9V, 12V, 15V, 19V and 20V

Standard Power profiles associated with USB Power adapters: 18W, 33W, 45W, 65W, and up to 100W (Power factor correction circuitry is required for power levels above 65W). 

SMPS (Switched Mode Power Supply)

Block diagram:

            The block diagram of SMPS is attached in image6.

Explanation:

Rectification stage

Introduction:

• It is mainly used to convert the AC mains voltage to ripple-free DC voltage by means of diodes. The output is an uncontrolled DC signal.
• Most of the power electronics applications such as switching dc power supplies, ac motor drives, dc servo drives, etc. use such uncontrolled rectifiers.
• The dc output voltage of a rectifier should be as ripple free as possible. Therefore, a large capacitor is connected which acts as a filter on the dc side
• The rectifiers are supplied directly from the utility source without a 50/60Hz transformer. The avoidance of this costly and bulky 50/60Hz transformer is important in most modem power electronic systems for a reduction in size and copper usage.
• Some of the components connected inline between the AC input and bridge rectifier include fuse, EMI filters, x-cap (for interference suppression), and common mode choke (to decrease common-mode noise which usually arises because of differences in ground references).
• Since most of the practical loads are nonlinear or inductive in nature, further explanation is carried out considering the same.

Working:

• The circuit diagram of full-bridge diode rectifier can be seen in the attached image 1.
• The supply voltage is Vs. The source voltage Vs is in series with its internal impedance, which is primarily inductive. To improve the line current, an inductor may be added in series on the Ac side. The overall inductance is named as Ls.
• We shall look at the working considering both Ls=0 and Ls=finite value
• When Ls=0,
  • For simple understanding, the circuit is redrawn in image 2.
  • The circuit consists of two groups of diodes, the top group with diodes I and 3 and the bottom group with diodes 2 and 4.
  • The current id (diode current which is basically an output current) flows continuously through one diode of the top group and one diode of the bottom group.
  • In the top group, the cathodes of the two diodes are at a common potential. Therefore, the diode with its anode at the highest potential will conduct id. That is, when Vs is positive, diode I will conduct id, and Vs will appear as a reverse-bias voltage across diode 3. When Vs goes negative, the current id shifts (commutates) instantaneously to diode 3 since Ls = O. A reverse-bias voltage appears across diode I.
  • In the bottom group, the anodes of the two diodes are at a common potential. Therefore, the diode with its cathode at the lowest potential will conduct id. That is, when Vs is positive, diode 2 will carry id and Vs will appear as a reverse-bias voltage across diode 4. When Vs goes negative, the current id instantaneously commutates to diode 4 and a reverse-bias voltage appears across diode 2.
  • The input and output voltage waveforms can be found in the image3.
  • In this case output voltage Vdo = 0.9*Vs.
• When Ls≠0,
  • Due to a finite Ls', the transition of the ac-side current is from a value of +Id to -Id (or vice versa) will not be instantaneous. The finite time interval required for such a transition is called the current commutation time or the commutation interval, and this process where the current conduction shifts from one diode (or a set of diodes) to the other is called the current commutation process.
  • The waveforms are like that of the previous case except that there is a slight delay in initial conduction.
  • The output voltage is like the previous case except that an area Au (lost due to current commutation) is lost in every half-cycle from the integral voltage. Therefore Vd = Vdo - (2*w*Ls*Id)/pi
    

Controlled DC Stage

Introduction:

• The dc-dc converters are widely used in regulated switch-mode dc power supplies. Often the input to these converters is an unregulated dc voltage, which is obtained by rectifying the line voltage, and therefore it will fluctuate due to changes in the line-voltage magnitude.
• Switch-mode dc-to-dc converters are used to convert the unregulated dc input into a controlled dc output at the desired voltage level.
• These DC-DC converters are very often used with an electrical isolation transformer in the switch-mode dc power supplies (SMPS) and almost always without an isolation transformer in the case of dc motor drives.
• Some of the non-isolated converters include Step-down (buck) converter, Step-up (boost) converter, Step-down/step-up (buck-boost) converter, Cuk converter, and Full-bridge converter. (image7)
• Some of the isolated converters include Flyback converter, Forward converter, Push-pull converter, Half-bridge a Full bridge converter.
• The maximum power ratings, their typical efficiency, and their applications are discussed in previous blog(part1).
• The DC-DC converter which is best suited for the USB power application includes an isolated Fly-back converter and a non-isolated buck-boost converter.
• Nonisolated and their corresponding isolated topology is as given below,

• Form the above-mentioned block diagram, an isolated DC-DC converter stage includes inverter chopper, output transformer, output rectifier, and filter.
• The basic application of a switch in a power converter is to control the duration of current flow in the circuit. By achieving the average output voltage and current can be controlled based on the desired value.
• Consider the circuit as shown in the image4. The average value Vo (output voltage) depends on Ton and Toff as shown in the corresponding image.

Basic Converter working:(explained using buck converter example)

• In dc-dc converters, the average dc output voltage must be controlled to equal the desired level, though the input voltage and the output load may fluctuate. Switch-mode dc-de converters utilize one or more switches to transform dc from one level to another. In a dc-dc converter with a given input voltage, the average output voltage is controlled by controlling the switch on and off durations (Ton and Toff).
• Consider the circuit shown in the image9. This is a basic buck converter without the filter circuit.
• When the switch is toggled between positions 1 and 2 with proper duty cycle, the desired output voltage can be obtained (in this case a stepped-down voltage).
• When this type of circuit is used without a filter, the output will be comprised of the DC components and AC components with a lot of harmonics.
• The output voltage waveform of this type of circuit comprising of both AC and DC components is attached in the image10.
• A filter must be designed with cutoff frequency fo<<<fs, where the average voltage of the waveform i.e. D*Vin will be obtained (which is a straight line with ripples. The ripple content can be minimized by properly designing the filter). (D = ton/Ts)
• Hence the circuit in image9 along with the inductor and a capacitor connected in series and parallel respectively on the output side acts a buck converter.
• Since it is a low pass filter, the components less than fo will be passed and reject the components in the Fourier series that are greater than fo. Hence it will reject the components with frequency fs and pass the dc component D*Vin. (which is nothing but the output voltage of a buck converter).
• One of the methods for controlling the output voltage employs switching at a constant frequency (hence, a constant switching time period Ts = Ton + Toff) and adjusting the turn-on the duration of the switch to control the average output voltage. In this method, called pulse-width modulation (PWM) switching, the switch duty ratio D, which is defined as the ratio of the on duration to the switching time period, is varied. The other control method is more general, where both the switching frequency (and hence the time period) and the on duration of the switch are varied. This method is used only in dc-dc converters utilizing force-commutated thyristors.
• The basic circuit for implementing PWM controlled converter is shown in the image5.
• In the PWM switching at a constant switching frequency, the switch control signal, which controls the state of the switch, is generated by comparing a signal-level control voltage Vcontrol with a repetitive waveform as shown in the image5. The control voltage signal generally is obtained by amplifying the error, or the difference between the actual output voltage and its desired value. The frequency of the repetitive waveform with a constant peak, which is shown to be a sawtooth, establishes the switching frequency. This frequency is kept constant in a PWM control and is chosen to be in a few kilohertz to a few hundred-kilohertz range. When the amplified error signal, which varies very slowly with time relative to the switching frequency, is greater than the sawtooth waveform, the switch control signal becomes high, causing the switch to turn on. Otherwise, the switch is off. In terms of Vcontrol and the peak of the sawtooth waveform Vsawtooth, the switch duty ratio can be expressed as

D = ton/Ts =Vcontrol/Vsawtooth

• The dc-dc converters can have two distinct modes of operation, continuous current conduction, and discontinuous current conduction. In practice, a converter may operate in both modes, which have significantly different characteristics. Therefore, a converter and its control should be designed based on both modes of operation.

Nonisolated Buck-Boost Converter:

• The main application of a buck-boost converter is in SMPS or regulated output power supplies, where a negative-polarity output may be desired with respect to the common terminal of the input voltage, and the output voltage can be either higher or lower than the input voltage.
• The buck-boost converter can be obtained by cascading a Buck converter (step down converter, where ideally output is equal to or less than the input) followed by Boost converter (step-up converter, where ideally output is equal to or greater than the input).
• The circuit diagram of a Buck-boost converter is attached in image8.
• When the switch is closed, the input provides energy to the inductor and the diode is reverse biased. When the switch is open, the energy stored in the inductor is transferred to the output. No energy is supplied by the input during this interval. In the steady-state analysis presented here, the output capacitor is assumed to be very large, which results in a constant output voltage Vo(t) ~ Vo
• In steady-state, the ratio of output to input voltages is the product of the output to input voltage ratios of the two converters in cascade (if switches in both converters have the same duty ratio).

Voutput/Vinput = D/1-D

where D = duty ratio (explained in the previous section)

• From the above-derived output voltage ratio, we can conclude that the output can either be greater than(boost) or less than(buck) the input voltage.
• There are two modes in which a buck-boost converter operates. Continuous conduction mode (CCM) and discontinuous mode of operation (DCM).
• Discontinuity occurs due to the following reasons,
• When the ripples are greater than the inductor current or capacitor voltage. As a result, the direction of current flow changes and discontinuity occurs.
• It occurs in DC-DC converters where unidirectional switches (diode, BJT, IGBT) are used.
• It also occurs when the converter is operating in light load conditions.
• The operating mode is decided based on load conditions and power requirements. This can be achieved by controlling the duty ratio and value of the passive electronic components used in the circuit(inductor).
• In DCM, the average output voltage decreases. Hence this mode is preferred when Low powered loads are used, or low energy is required. When the diode is used as a rectifier (as shown in the circuit diagram), the converter goes to DCM. When a synchronous rectifier is used, the operation depends on the driving signal.
• In CCM, the average output voltage increases. This mode is preferred when the load requires high power.
• When the resistance of the load > resistance of the circuit, the circuit operates in CCM and vice versa.

Flyback converter (Isolated Buck-Boost Converter)

• The overall block and the role of isolated DC-DC converter are attached in image13.
• The basic working of an isolated converter is as follows,
  • The dc-dc converter block as shown in the image13 converts the input dc voltage from one level to another dc level. This is accomplished by high-frequency switching, which produces high-frequency ac across the isolation transformer.
  • The secondary output of the transformer is rectified and filtered to produce output Vo(shown in image13) The output of the dc supply is regulated by means of feedback control that employs a PWM controller as discussed in the previous section, where the control voltage is compared with a sawtooth waveform at the switching frequency. The electrical isolation in the feedback loop is provided either through an isolation transformer as shown or through an optocoupler.
• Classification of isolated DC-DC Converter based on their transformer core utilization,
• Unidirectional core excitation where only the positive part (quadrant 1) of the B-H loop is used (Fly Back and Forward Converter).
• Bidirectional core excitation where both the positive (quadrant 1) and the negative (quadrant 3) parts of the B-H loop are utilized alternatively (Pushpull, Half bridge and forward converter).
• Nonisolated converter is converted to an Isolated converter by including Transformer where the average value of inductor voltage becomes zero. Hence in Buck-Boost converter, transformer is placed after the inductor where according to the waveform at that point, the average value of inductor voltage is zero.
• Working:
  • The basic circuit diagram of open-loop flyback converter is attached in image14.
  • During the switch T1 is in ON position, the current builds up in the transformer primary (and thus storing energy). When the switch is turned OFF, the polarity of primary and secondary coil voltages is reversed. Now the diode D1 is in forward biased and the energy stored in the transformer is transferred to the Capacitor (C1), sequentially to the load.
  • When the switch T1 is in ON position, the voltage across diode D1, which is reverse biased is given as,

Vd = Vo + (Vs * Ns/Np)

When T1 is ON, Diode D1 is reverse biased. Hence voltage across it is the sum of output voltage plus the reflected input voltage.

• When the switch T1 is in OFF position, the voltage across T1is given as,

Vt1 = Vs + (Vo * Np/Ns)

When T1 is OFF, switch T1 is reverse biased (open). Hence voltage across it is the sum of input voltage plus the reflected output voltage.

• The waveforms are attached in image15.
• It has a low parts count.
• Careful design of the transformer turns ratio between primary and secondary that enable the output to be higher or lower to the input.
• A Flyback converter can support multiple outputs by adding more windings to the transformer.
• The Flyback converter uses the single magnetic of a common reference of a transformer behave as the coupled inductor, this transformer combines the functions of energy stored, energy transferred, and isolation. So, the need for a separate LC filter on each output is laminated. This reduces the overall cost of the flyback converter.
• It is important to note that the diode and switch should not conduct at the same time.
• Different modes of operation of the Flyback converter:
  • Frequency modulation (FM) and Amplitude Modulation (AM).
  • Discontinuous Conduction Mode (DCM).
  • Valley Switching.
  • Quasi-Resonant
  • Continuous Conduction Mode.
  • Boundary conduction Mode.

DCM:

• When the power stage is designed in such a way to allow the transformer to completely demagnetize during each switching cycle. The simplest form of a DCM flyback is designed with a fixed switching frequency and modulates the peak current to support the load demands.
• At the start of the switching period, the on-time begins, and the primary side current ramps up from zero.
• At the end of the on-time, the primary current of collapses back to zero, and the current flows to the secondary windings. It begins at its peak proportional to the turn’s ratio and ramps down to zero, completely demagnetizing the transformer during every switching cycle.
• After the demagnetizing time, there is a delay before the primary side switch turns on again to start the next switching cycle. This delay is referred to as dead time. During this portion of the switching period, neither the diode nor the MOSFET is conducting. This dead time, where the transformer is completely demagnetized and no current is being conducted, is why this operating mode is known as discontinuous or DCM.
• During this dead time, a resonant ring is generated by the interaction between the primary inductance of the transformer and the parasitic capacitance at the switch node. A converter in deep discontinuous mode can have a dead time long enough for the resonant ringing to dampen completely, at which point the drain to source voltage will have settled to be equal to the input voltage.
• A flyback is operating in DCM when the power stage is designed in such a way as to allow the transformer to completely demagnetized during each switching cycle.
• At the start of the switch period, the in-time begins, and the primary side current ramps up from zero. At the end of the no-time, the primary current collapses back to zero, and the current flows to the secondary windings. It begins at its peak proportional to the turn’s ratio and ramps down to zero, completely demagnetizing the transformer during every switching cycle.
• After the demagnetizing time, there is a delay before the primary side switch turns on again to start the next switching cycle. This delay is referred to as dead-time or resonant time. During this portion of the switching period, neither the diode nor the MOSFET is conducting.
• The waveform of the Flyback converter operating in DCM is attached in image16.
• Advantages of DCM: The advantages of DCM flyback are that there are no reverse recovery losses in the output rectifier because it’s able to ramp down to zero amps during every switching cycle.  The primary inductance is the lowest out of all the flyback, which may result in a smaller transformer. A DCM flyback is inherently more stable because it doesn’t have a right-half-plane to zero in its transfer function.
• Disadvantages DCM: DCM flyback does have the disadvantage of very large ripple currents, which may require large EMI filters. Fixed frequency DCM flyback has higher losses because they can turn off the switch when the drain to source voltage may be relatively high. It can be ringing higher than the input voltage now of turn-off, this could contribute a considerable hit to efficiency, as the switching losses are proportional to the square of this voltage.

Valley Switching:

• Valley switching is a specialized form of discontinuous conduction mode and requires a controller that is specifically designed to detect when the resonant ring during the dead time is at a low point.
• Before turning the MOSFET on to start the next switching cycle, minimizing switching losses.
• In order to maintain the required average output power, the controller will modulate the switching frequency by skipping one or more valleys from one cycle to the next.
• Controllers that modulate the frequency to meet the average load demand every cycle are operating in FM (frequency modulation) mode. This is sometimes also called frequency fold back because as the load demand is decreased the switching frequency is also decreased or folded back.
• Valley switching can occur at any resonant valley during the dead time as long it’s large enough for the control to detect. The switching waveforms may appear to dither as the controller adjusts its dead time in its search for the nearest valley.
• The waveform of the Flyback converter operating in Valley switching mode is attached in image17.
• Advantages of Valley Switching: Valley switch flyback has all the advantages of traditional DCM flyback with the bonus of lower switching losses due to consistently turning the MOSFET off when the drain to source voltage is at a low value. This also helps to reduce the turn-on current spike at the current sense resistor. The dithering produced by valley skipping helps to reduce EMI.
• Disadvantages of Valley Switching, Unfortunately, valley skipping will result in higher output voltage ripple. Also, valley switching is ineffective if the converter is operating in the deep discontinuous mode as the controller will not have enough of a signal to detect a valley

Quasi-Resonant Mode:

• Quasi-resonant mode or QR may be referred to as critical condition mode or transition mode.
• Quasi-resonant operation is a specific valley switching the operating mode of DCM where the switching occurs on the very first and deepest resonant valley.
• QR delivers the maximum amount of power by adjusting both the peak current and the switching frequency to turn the MOSFET on at the first resonant valley for minimal losses.
• QR controllers operate in AM and FM mode at the same time to meet the demands of energy transfer. QR controllers will decrease the switching frequency as the load increases. This is just the opposite of the frequency fold back mentioned earlier.
• Most Valley switching controllers can operate in Quasi-resonant mode but only at the specific operating point of maximum load and minimum input voltage when designed accordingly.
• This limited QR range of operation is due to the control method used in the valley switching controllers, where only the frequency is modulated. Not both the frequency and the peak current like in dedicated QR controllers.
• The waveform of the Flyback converter operating in QR mode is attached in image18.
• Advantages of QR mode: QR mode converters switch at the lowest drain to source voltage, they achieve the lowest possible switching losses and have high efficiency over the entire operating range. This is a soft-switching converter only small EMI filters are needed.
• Disadvantages of QR mode: QR converters are difficult to compensate due to the wide peak current and switching frequency ranges. A considerable phase margin is required to maintain stability over the entire operating range.

CCM:

• CCM refers to continuous conduction mode. A continuous current is always flowing in the transformer during each switching cycle.
• When the MOSFET is turned on the primary current ramps up. But it doesn’t start from zero amps as in DCM. In CCM the current ramps from an offset that is due to residual energy that is continuously maintained in the transformer.
• When the switches turned off energy is transferred across the secondary and the transformer demagnetizes resulting in the secondary side current ramping down. But it does not ramp all the way to zero amps.
• Residual energy is maintained in the transformer. The next switching cycle begins before the current is completely depleted.
• As shown, the current waveform on both the primary and the secondary is trapezoidal in shape. This is sometimes referred to as a ramp on a step.
• Note that there is no dead-time in CCM. Current is always being conducted somewhere in the transformer but also note that despite continuously conducting current the MOSFET and the diode do not conduct at the same time.
• As the load demand decreases the store of residual energy the step portion of the waveform decreases.
• CCM flyback transformers are designed based upon the ripple current or ramp portion of the waveform which is considerably less than the ripple seen in DCM flyback. Controllers specifically designed for Valley switching will not operate in CCM as there is no resonant ring available and the transformer is not allowed to fully demagnetize.
• The waveform of the Flyback converter operating in CCM mode is attached in image19.
• Advantages of CCM: Lower peak currents mean smaller filter components. The advantages of CCM are the small ripple and RMS current which result in lower capacitor losses. These lower current also help lower conduction and turn-off losses when compared to DCM flyback. Lower peak current means smaller filter components.
• Disadvantages of CCM: The most noted disadvantage of CCM flyback is the presence of a right-half-plane zero in the power stage transfer function, this limits the bandwidth of the control loop and will impact the converter’s dynamic response. Also, CCM flyback require a larger inductance which may require a large magnetic component.

Topics i would be covering in my next blog

• Different closed loop topologies in flyback converter.
• 4 switch Buck-Boost Converter.

People who are interested to learn more than discussed here and if there are any mistakes or errors in the written blog, please let me know in the comments section.

Regards

Abhilash P

Various definitions on What is Power electronics?

• Power Electronics is the study of switching electronic circuits in order to control the flow of electrical energy. It is the technology behind switching power supplies, power converters, power inverters, motor drives, and motor soft starters.
• Power electronics is the application of solid-state electronics for the control and conversion of electric power. It applies to both the systems and products involved in converting and controlling the flow of electrical energy, allowing the electricity needed for everyday products to be delivered with maximum efficiency in the smallest and lightest package.
• Power Electronics is basically an interface between unstable and stable Electrical Energy. Electrical Energy (AC or DC, voltage or current) obtained from any sources can be converted into well-regulated AC or DC, Voltage or Current of any desired level.
• The task of power electronics is to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads.

Different Applications of Power Electronics:

• Residential: Refrigeration and freezers, Space heating, Air conditioning, Cooking, Lighting Electronics (personal computers, other entertainment equipment).
• Commercial: Heating, ventilating and air conditioning, Central refrigeration, Lighting, Computers and office equipment, Uninterruptible power supplies (UPSs), Elevators.
• Industrial: Pumps, Compressors, Blowers and fans, Machine tools (robots), Arc furnaces, induction furnaces, Lighting, Industrial lasers, Induction heating, Welding.
• Transportation: Traction control of electric vehicles, Battery chargers for electric vehicles, Electric locomotives, Street cars, trolley buses, Subways, Automotive electronics including engine controls.
• Utility systems: High-voltage dc transmission (HVDC), Static var compensation (SVC), Supplemental energy sources (wind, photovoltaic), fuel cells, Energy storage systems, Induced-draft fans and boiler, feedwater pumps.
• Aerospace: Space shuttle power supply systems, Satellite power systems, Aircraft power systems.
• Telecommunications: Battery chargers, Power supplies (dc and UPS).

Power Electronic Converters:

• The power converter usually consists of more than one power conversion stage where the operation of these stages is decoupled on an instantaneous basis by means of energy storage elements such as capacitors and inductors. Therefore, the instantaneous power input does not have to equal the instantaneous power output. Thus, a converter is a basic module (building block) of power electronic systems. It utilizes power semiconductor devices controlled by signal electronics (integrated circuits) and possibly energy storage elements such as inductors and capacitors.
• Based on the form (frequency) on the two sides, converters can be divided into the following broad categories:

1. AC TO DC (Rectifiers).
2. DC TO AC (Inverters).
3. DC TO DC (Choppers).
4. AC TO AC (Cycloinverters) (controlled voltage and frequency).
5. AC TO AC (AC voltage controller) (controlled voltage)

• Further insight can be gained by classifying converters according to how the devices within the converter are switched.

1. Line frequency (naturally commutated) converters where the utility line voltages present at one side of the converter facilitate the turn-off of the power semiconductor devices. Similarly, the devices are turned on, phase-locked to the line voltage waveform. Therefore, the devices switch on and off at the line frequency of 50 or 60 Hz.
2. Switching (forced-commutated) converters, where the controllable switches in the converter are turned on and off at frequencies that are high compared to the line frequency. Despite the high switching frequency internal to the converter, the converter output may be either dc or at a frequency comparable to the line frequency. As a side note in a switching converter, if the input appears as a voltage source, then the output must appear as a current source or vice versa.
3. Resonant and quasi-resonant converters, where the controllable switches tum on and/or tum off at zero voltage and/or zero current.

Linear and Switched Mode Converters:

• Block Diagram and Circuit diagram of Linear regulated Power Supply can be seen in attached image1 and 2.
• Block Diagram and circuit diagram of Switched Mode Power Supply can be seen in attached image 3 and 4.

Some pros and cons of using Power Electronic Converters:

Power Electronic Switching Devices:

• Power switches play a main role in power electronic converters. They operate in 2 states, Conducting state (that means the switch is closed) and Blocking state (that means the switch is off).
• Based on their control input requirements, they are categorized into 3 types,

• Furthermore, they are also categorized into 3 types based on turn-on and turn-off control,

• The following characteristics are desired in a power semiconductor switch,

1. Small leakage current in the off state.
2. Small on-state voltage Von to minimize on-state power losses.
3. Short tum-on and tum-off times. This will permit the device to be used at high switching frequencies.
4. Large forward- and reverse-voltage-blocking capability.
5. High on-state current rating. In high-current applications, this would minimize the need to connect several devices in parallel, thereby avoiding the problem of current sharing.
6. Positive temperature coefficient of on-state resistance. This ensures that paralleled devices will share the total current equally.
7. Small control power required to switch the device. This will simplify the control circuit design.
8. Capability to withstand the rated voltage and rated current simultaneously while switching. This will eliminate the need for external protection (snubber) circuits across the device.
9. Large dv/dt and di/dt ratings. This will minimize the need for external circuits otherwise needed to limit dv/dt and di/dt in the device so that it is not damaged.

• Comparison of different switches,

Switched Mode Power Supply (SMPS):

• The main components of an SMPS consist of a rectification block (which is used to convert AC line voltage to controlled DC voltage) and a DC-DC converter block (which is used to convert varying DC voltage to fixed DC voltage based on the load demand).
• The different types of the rectifier and their classification block diagram can be seen in the attached image 5.
• Typically for an SMPS application, we use Single-phase uncontrolled full-wave bridge rectifier.
• The classification of DC-DC converters can be seen in attached image 6.
• The typical power ratings and the applications of some of the DC-DC converters are as mentioned below,

• For a typical USB application, we use an isolated Fly-back converter.
• The basic circuit diagram of Fly-back is attached in image7

The basic operation of Fly-back converter:

• High Input voltage Vin is rectified using a diode bridge rectifier.
• The rectified voltage is filtered using necessarily designed passive electronic components.
• Then obtained DC voltage is switched at high frequencies using switch S1. The main objective of switching is to convert the constant DC voltage to pulsating DC voltage and pass it through high-frequency transformer, where the DC voltage is stepped down to required levels.
• The stepped down pulsating DC voltage is rectified and passed through a filter and is fed to the load.
• More about the working of closed-loop DC-DC converters and their in-depth role in USB application with detailed circuit explanations will be spoken in my upcoming blog.

(credits: Ned Mohan. Conveters, Applications and Designs)

Topics I will be discussing in part 2,

• USB power specifications.
• USB Power Supply.
• Primary and Secondary control of Fly-back converters.
• Circuit level understanding of 2-switch and 4-switch Buck-Boost converter.

Regards

Abhilash P

     The attached document consists of an offline guide to Cypress EZ-PD Type C USB Products. This document can also be used as an offline guide for customers by onsite sales and field application engineers.

Regards

Abhilash P

The CCGx Host SDK and Power SDK contains a noboot project along with the main firmware project for each firmware example to allow debugging. This is done using the Debug option on PSoC Creator through a SWD debugger such as MiniProg3 or MiniProg4. However, we cant use debug mode for the main firmware project directly since it contains the bootloader that doesnt allow the debugging the application.

To debug the main firmware project with the bootloader, follow the steps below. The CCG3 (CYPD3125-40LQXIT) notebook project from the Host SDK is used as an example here.

1. Go to the Design Wide Resources file and assign the Debug Select to SWD. Make sure that the SWD pins for the device are not assigned to anything else and are free for debug.

2. Build and program the .hex file onto the device. You can use the Program option on PSoC Creator for programming it as well.

     If the device is not acquired, configure the port settings as shown below.

3. With the same setup connected, use the Attach to Running Target option to acquire the device.

4. Since the firmware is already running on the device, the debugger will access it from the point it was attached. The Reset option can be used to issue a Soft Reset to the device and bring the firmware execution to main() again.

Version: *R

West Bridge®: Astoria™ USB and Mass Storage Peripheral Controller

Features

• Multimedia device support
• Supports Microsoft® Media Transfer Protocol (MTP) with optimized data throughput
• Simultaneous Link to Independent Multimedia (SLIM®) architecture, enabling simultaneous and independent data paths between the processor and USB, and between the USB and mass storage
• High-speed USB at 480 Mbps
  • USB 2.0 compliant
  • Integrated USB switch
  • Integrated USB 2.0 transceiver, smart serial interface engine
  • 16 programmable endpoints
• GPIF (General Programmable Interface)
• For more, see pdf

Functional Overview

Turbo-MTP Support

Turbo-MTP is an implementation of Microsoft’s MTP enabled by West Bridge. In the current generation of MTP-enabled mobile phones, all protocol packets needs to be handled by the main processor. West Bridge Turbo-MTP switches these packet types and sends only control packets to the processor, while data payloads are written directly to mass storage, thereby bringing the high performance of West Bridge to MTP.

CYPD3177(BCR) has provided four sets of resistor divider networks are used to determine the voltage and current range that the EZ-PD BCR device will negotiate

with the USB Type-C power adapter. However, if it still cannot meet your requirement, you can change the PDO through its I2C register.

This blog gives a breif introduction on how to change the BCR register based on BCR HPI Spec.

1. Hardware Connection

Figure 1

Connect SCLK and SDAT of MiniProg to CY4533 as is shown in Figure 1. Set the rotary switch (SW1) to position 1 so CY4533 support 5V/0.9A by default. Use a CY4500 EZ-PD Protocol Analyzer to capture the cc communication between CY4533 and the power adapter.

Figure 2

As is shown in Figure 2, CY4533 request 5V/0.9A due to the max requesting VBUS set by rotary switch is 5V/0.9A.

2. Send I2C command in Bridge Control Panel to control BCR

Figure 3

Check the PD_STATUS register first. The value of PD_STATUS register is 00 A4 05 00. It means the explicit contract has been established between BCR and the charger. BCR is acting as a power sink and the two device both supports PD 3.0. To replace the default sink PDO, write the corresponding packet into the data memory start from 0x1800. For Byte 0-3, ASCII string “SNKP” (i.e 0x50 0x4B 0x4E 0x53) must be sent to make BCR update its sink PDO list. In this example, PDO 0 is set to 5V/0.9A and PDO 1 is set to 15V/1.75A. The remaining bytes are set to 0 because not all 7 PDOs are used.  Refer to Section 6.4 of Universal Serial Bus Power Delivery Specification for the description of Fixed Supply PDO. Figure 3 is the I2C commands sent and response from BCR.

Figure 4

After enabling the PDO0 and PDO1 mask by sending command to SELECT_SINK_PDO register, BCR will re-negotiate the PD contract with the power adapter. PD_RESPONSE register should be checked after sending command on command registers. 0x02 is the code for successful operation.CC communication is captured by CY4500 in Figure 4.