Sorry if the topic is confusing... What I am looking for is some advice on the construction of a power supply for a small transmitter.
I have a radio transmitter which is designed to to sit on a device which has a duty cycle of ~1%, so can sit unused for a period of time. It's switch controlled, and I need to send a radio signal from this device when it gets pressed used.
The design constraint is that the device may only be on for second of two, and I want to be able to pull enough power from the device to transmit for 3 seconds. This means having to store energy in a capacitor (I can't use a battery due to space constraints) and have it discharge over the period of 3 seconds.
The transmitter is ~4mA when on. The device has a power supply of 6V AC, which I will rectify to get 9.1V DC. I then need to smooth this and use a voltage regulator to bring it down to 5v DC (+/- 5%). That's no problem, all that works...
The problem is that I need to be able to supply this 5V for 3 seconds, and not have it drop off in a gradual slope, I need definate ON/OFF switching. With the present circuit, I get a wave while the capacitor discharges...
The circuit goes:
AC -> Bridge Rectifier -> Smoothing Cap 22uF -> Storage Cap 1000uF -> 5V Regulator -> Smoothing Cap .01uF -> Transmitter.
Can you recommend any way of inproving this to eliminate the gradual dropoff?
Sorry if it's complex. I will get around to doing a circuit/drawing soon...
I have a radio transmitter which is designed to to sit on a device which has a duty cycle of ~1%, so can sit unused for a period of time. It's switch controlled, and I need to send a radio signal from this device when it gets pressed used.
The design constraint is that the device may only be on for second of two, and I want to be able to pull enough power from the device to transmit for 3 seconds. This means having to store energy in a capacitor (I can't use a battery due to space constraints) and have it discharge over the period of 3 seconds.
The transmitter is ~4mA when on. The device has a power supply of 6V AC, which I will rectify to get 9.1V DC. I then need to smooth this and use a voltage regulator to bring it down to 5v DC (+/- 5%). That's no problem, all that works...
The problem is that I need to be able to supply this 5V for 3 seconds, and not have it drop off in a gradual slope, I need definate ON/OFF switching. With the present circuit, I get a wave while the capacitor discharges...
The circuit goes:
AC -> Bridge Rectifier -> Smoothing Cap 22uF -> Storage Cap 1000uF -> 5V Regulator -> Smoothing Cap .01uF -> Transmitter.
Can you recommend any way of inproving this to eliminate the gradual dropoff?
Sorry if it's complex. I will get around to doing a circuit/drawing soon...