Stable 5 Volt supply

[trastikata]

1. 7805 and 1117 regulators are LDO regulators and the 7805 needs at least 2.2v difference in the voltage, where the 1117 has about 1.5v dropout. Are you sure that your main supply can keep 7,2 (6.5) volts at that load? With other words measure your input voltage under load.

2. Do you have a heatsink on your regulator? At 350ma load and 5v dropout, the 7895, even the to-220 case, will be overheating in matter of seconds if there's no heatsink, the 1117 will probably burn out.

3. 1117 has 3.3, 2.5, 1.2 and adj output variations - are you sure you didn't get the 3.3 version?

4. What is the circuit, can you share it? At those currents you should go for a switching mode regulator and not a LDO type.

 

[adwnis123]

In the case of LD1117 there are two versions. One is for 3.3 volts and other for 5volts. In both cases it will require at least 8 volts in the input side to work efficiently. 104 or 100nf has nothing to do with the voltage drop unless it has a leakage. You are using LD1117 but please let me know what is written except that on the device. 3.3 or 5.0?
Also let me know what voltage is your circuit built for? 3.3 or 5 volts?

The LD1117 is for 3.3 output.
The circuit I want to supply with LM7805 is 5 Volt.

 

[adwnis123]

1. 7805 and 1117 regulators are LDO regulators and the 7805 needs at least 2.2v difference in the voltage, where the 1117 has about 1.5v dropout. Are you sure that your main supply can keep 7,2 (6.5) volts at that load? With other words measure your input voltage under load.

2. Do you have a heatsink on your regulator? At 350ma load and 5v dropout, the 7895, even the to-220 case, will be overheating in matter of seconds if there's no heatsink, the 1117 will probably burn out.

3. 1117 has 3.3, 2.5, 1.2 and adj output variations - are you sure you didn't get the 3.3 version?

4. What is the circuit, can you share it? At those currents you should go for a switching mode regulator and not a LDO type.

1. I use 10 volts to supply the lm7805.
2. No I do not. I touch it, it is not hot.
3. Yes I have the 3.3 output version
4. It is a simple circuit with PIC that sends data over rs232. I do it from scratch, I do not have drawings.

 

[trastikata]

1. I use 10 volts to supply the lm7805.

Ok, it is 10v nominal, but with 350ma load (as you said) this could drop bellow 7.5v - that's why asked you to measure the supply voltage under load.

2. No I do not. I touch it, it is not hot.

If the supply voltage is 10v, output is 5v and the load is 350ma it should be burning hot after 10-15 sec.

4. It is a simple circuit with PIC that sends data over rs232. I do it from scratch, I do not have drawings.

Why is it drawing 350ma in that case, this is a lot for only a PIC with RS232 enabled?

 

[adwnis123]

Ok, it is 10v nominal, but with 350ma load (as you said) this could drop bellow 7.5v - that's why asked you to measure the supply voltage under load.


If the supply voltage is 10v, output is 5v and the load is 350ma it should be burning hot after 10-15 sec.


Why is it drawing 350ma in that case, this is a lot for only a PIC with RS232 enabled?

I use a zigbee that draws 250 ma current

 

[ArticCynda]

What kind of zigbee transceiver are you using? An integrated type (i.e. CC2530) or a discrete module (i.e. Xbee)?

 

[adwnis123]

What kind of zigbee transceiver are you using? An integrated type (i.e. CC2530) or a discrete module (i.e. Xbee)?

I use this one: SHUNCOM SZ05-ADV

**broken link removed**

 

[adwnis123]

I use this one: SHUNCOM SZ05-ADV

**broken link removed**

I put supply 15 volt and I get at the output of the LM7805, 4.61 Volt (0.11 Volts more than I supply with 10 Volts) I didn't use the zigbee module.

What is going wrong????

 

[FvM]

I fear it's difficult to see from a distance what you are doing wrong. Maybe just a defective multimeter?