TE Connectivity - PolyZen Device Helps Protect Portable Electronics
The mobile functionality of portable media players (PMPs), navigation devices, smart phones, play stations and other batterypowered portable equipment offers consumers an increasingly connected lifestyle between their home, office, and vehicle. However, every time these products are connected or disconnected, they may be exposed to circuit damage caused by user error, wrong supply voltages, or voltage or current transients.
Transient Protection Design Considerations
Transient protection is critical when designing peripherals that may be powered off computer buses and automotive power buses. On computer buses, inductively generated voltage spikes can exceed 8V on the 5V line and 16V on the 12V line, which can damage unprotected peripherals. With the advent of low-cost third party AC-to-USB converters, and car cigarette lighter-to-USB converters, the potential for transients to be seen on computer buses continues to increase.
PolyZen Helps Protect Portable Electronics
Traditional clamping diodes represent the simplest circuit protection solution for portable electronics. However, in order to withstand the potential power output of a non-approved charger while still providing resettable protection, this diode must be capable of dissipating nearly all of the power that a non-approved charger could deliver. The resultant protection solution would therefore require both a large diode and significant heat-sinking infrastructure.
The latest generation of clamping diodes, the PolyZen device, offers designers the simplicity of a traditional clamping diode while obviating the need for significant heat sinking. This single device solution helps protect against damage resulting from the use of improper power supplies. It also helps provide transient suppression, reverse bias protection, and protection from damage caused by overcurrent events.
As shown in Figure 1, the PolyZen micro-assembly incorporates a stable Zener diode for crisp voltage clamping and a resistively non-linear polymeric positive temperature coefficient (PPTC) layer. The PPTC layer responds to either diode heating or overcurrent events by transitioning from a low- to a high-resistance state. In the event of a sustained high-power overvoltage condition, the tripped PPTC element limits current and generates a voltage drop to help protect both the Zener and the follow-on electronics - effectively increasing the diode’s power-handling capability.
The PolyZen device is particularly effective at clamping and smoothing inductive voltage spikes. In response to an inductive spike the Zener diode element shunts current to ground until the voltage is reduced to the normal operating range. In the case of a wrong voltage power supply, the device clamps the voltage, shunts excess power to ground, and eventually locks out the wrong supply. The relatively flat voltage versus current response of the device helps clamp the output voltage, even when input voltage and source currents vary.
Benefits
- Helps shield downstream electronics from overvoltage transients and reverse bias.
- Helps reduce design costs with single component replacement.
- Analog nature of trip events miminizes upstream inductive spikes.
- Power handling on the order of 30 watts.
- Available hold currents up to 2.3A.
