Peak Detector Questions

1. You can use both the collector and emitter as load drivers. Search for transistor load driving on google. 2. Pwm signals are widely applicable for dc coupled loads. Also I would suggest using either a relay as driver or either a transistor and not both. This to decrease components and costs, because relays are quite expensive. Hope this helped

oh good! I was worried because this circuit doesn't seem to work with the load on the collector side. I originally had only the relay as the driver. Unfortunately the coils of the relay acted as a resistor in parallel to the 30k which reduced the total resistance to about 375 ohms and caused the capacitor to discharge much quicker. So I had to use the NPN to drive the relay. If cost is the only problem with having both as the driver, then I'll keep it this way because it was requested that the user hears a "click" when activated. Thanks a lot for your answers!

1. You should put the load at the transitors collector.The reason the circuit didn't work when you put the load on the transistors collector is that a lot of current flows through the base to the emitter, discharging the capacitor in an instant, because you probably didn't add a resistor to limit the current. Just put a resistor (for example 10k) before the base and you can put the load at the collector. 2. Driving the relay with a transitor is necessary in many cases. Your statement " Unfortunately the coils of the relay acted as a resistor in parallel to the 30k which reduced the total resistance to about 375 ohms and caused the capacitor to discharge much quicker." is completely right just like your calculation! It almost always a good idea to seperate the logical and mechanical/medium-high power parts(like a relay) with a transistor. You've got that part completely right. 3. "I'm new to peak detectors so did I use this peak detector with the correct application? If not, what would you suggest to convert a PWM signal to power something requiring DC voltage?" I'm not really shure what you want to do with your circuit. Your circuit is checking for an PWM signal and if there is one it allows your second voltage source(DC) to power the relay powering an LED. If deactivated the signal, the voltage would sloooowly drop until the transistor is deactivated again. You 're not taking the energy from the PWM signal to power the relay, it's provided by the second voltage source, if that was your goal, you'd need a different circuit . How do you want to use the circuit? 4. If you ever control some high power device (headlight, motor [or even something mains-operated]) with a relay please completely seperate the circuits(the relay should be the only part that is connected two both circuits.) And if you don't control high power devices you should keep in mind that a transistor would work as well (unless really want to hear the relays clicking noise of course ;D) 5. Lol that's a lot of text. I hope it helps anyway. :D

Yes it helped a lot! Thanks a lot JasCraft for the good explanations! From 1... "you should put the load at the transistors collector" is it because since a lot of current flows through the base to the emitter, putting a load in series can "disrupt" the current flow which will inadvertently cause the transistor to operate inefficiently? From 3... "I'm not really sure what you want to do with your circuit" The square wave source is simulating a specific signal that a seat heater module is creating to power seat heaters in a vehicle. I'm splicing into that module's output to power my other heaters (which require a DC voltage). This way, when the user presses the button on the dashboard to turn on the seat heaters, my other heaters I retrofitted are activated as well :)