How many voltage regulators there are in a typical cordless phone?

Thread Starter

xchcui

Joined May 12, 2014
203
Hi.

I know that there is one voltage regulator,which is actually the battery charging controller,that regulates the voltage from the power adaptor to a value that suitable for charging the batteries.But is there another voltage regulator that regulates the voltage for the receiver/transmiter,the microphone/speaker etc.The other components in the base unit need different voltage,don't they?
 

wayneh

Joined Sep 9, 2010
17,152
The other components in the base unit need different voltage, don't they?
I'm sure it depends on the model of phone, but not necessarily. If the designers are told that the phone will have a, say, 5V regulated supply, they'd likely do all they can to make their sub-circuits work on that voltage to avoid using more components than necessary. Many devices - I don't know about phones - will have a single power supply section that establishes all the different voltages that are needed for the device. For instance a computer power supply offers +5V, +12V and -12V.
 

Audioguru

Joined Dec 20, 2007
11,249
A cordless phone does not need a voltage regulator. The circuit in the phone is designed to work from a fully charged battery voltage and also when the battery is almost dead. Its battery charger uses a resistor to limit the current and the wall wart is also not regulated and powers the charging resistor perfectly. A smart phone has a voltage regulator and a proper battery charger IC.
 
There was a time when rechargeable batteries could tolerate carelessness. Cheap 'wall wart' DC adapters usually provided much higher voltage than the label states. So 3 nicads in series might receive 6 or 7or 8 volts, even though they produce under 4V.
 

Audioguru

Joined Dec 20, 2007
11,249
A cheap Wall Wart produces its rated voltage when the electricity voltage is correct and when the wall wart has its rated load. Of course its voltage is higher with less load current or no load. The Ni-Cad or Ni-MH cells will never charge to higher than 1.4V to 1.5V per cell. The series current-limiting resistor limits their current and heating.
 

Thread Starter

xchcui

Joined May 12, 2014
203
Audioguru,my intention was refer more to the base unit.I understand that the handest is powered by the battery,but the base unit is received power from the wall wart.
I didn't understood the limit resistor technique.As you mentioned,wall wart adaptor is not regulated,so cordless phone that rated at 9vdc might get different value of voltage from the wall wart,even 11.5vdc at the nominal current consumption.Do you mean that the current limit resistor fits to that different value of voltages?and what about the other components in the base unit,what does limit the changing voltage from the wall wart to them?
 

Lo_volt

Joined Apr 3, 2014
174
In the base unit, there's likely to be a single power supply that powers the transmitter/receiver as well as the speaker amplifier.
It's a bit pointless to regulate power to the contacts that supply power to the handset as those contacts are likely to have inconsistent connection impedance due to corrosion, dirt, pressure or lack of pressure on the contacts, etc. It would make sense to pass through whatever the wall wart can supply and regulate it in the handset. If I were designing the phone, I'd also fuse the supply to those contacts.
 

Audioguru

Joined Dec 20, 2007
11,249
The battery regulates the voltage in the handset and there is nothing in the base unit that needs voltage regulation.
If you use a wrong wall wart with a voltage that is too high then the device it powers might be damaged.

The wall wart is selected so that the normal current in the phone base station plus charger gives roughly the correct voltage. If the battery has 3 cells then its fully charged voltage is 1.4V or 1.5V x 3= 4.2V to 4.5V then if the wall wart produces 9VDC and the allowed trickle charge current of the battery is 30mA (1/10th its mAh rating) then Ohms Law calculates the current-limiting resistor to be (9V - 4.2V)/30mA= 160 ohms. The current will be a little higher when the battery is almost dead at 3V.

But since a voltage regulator IC is cheap then they might use one or two.
 
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